In conventional analog circuit function verification, an analog circuit simulator, such as one with Simulation Program with Integrated Circuit Emphasis (SPICE, registered trademark) is used. Although such analog circuit simulators can calculate analog properties with high accuracy, an enormous amount of memory is used for the computation. Further, since the number of calculation steps is great and each step is detailed, verification using a typical operation model consumes at least several tens of thousands times more time for the verification of large-scale circuits and therefore, such analog circuit simulators cannot be used. As a result, verification using an operation model describing the analog circuit in hardware description language is commonly performed.
For example, concerning matrix constant formularization of circuit partitioning for circuit simulation where a circuit is partitioned into blocks, the partitioned circuit is compiled, current variables of an element that is independent of current variables between nodes outside a block are excluded from internal variables of the block, and simulation is performed (for example, refer to Japanese Laid-Open Patent Publication No. H6-124317). According to another technique, to simulate by numeric computation, the transient state of the waveform of a signal in a circuit having both an analog circuit and digital circuit, the analog circuit is partitioned into circuit blocks and modeled (for example, refer to Japanese Laid-Open Patent Publication No. 2010-92434).
Nonetheless, in the verification of analog circuit function, the analog circuit has to be replaced with an operation model that is of a high level of abstraction and described in hardware description language, and then simulated. However, a problem arises with approaches using hardware description language used for large-scale verification. The directions of signals are clearly defined by input and output definitions and consequently, interactions with elements outside the model, the function of circuits having impedance, and the like cannot be expressed by hardware description language.
For example, in the case of a circuit configuration having a given impedance and in which the input of a grounded resistor is connected to the output of an operational amplifier, if the downstream circuit connected to the output of the operational amplifier is not determined, the voltage/current of the output and input nodes cannot be defined. Thus, analog circuit simulators have been used for verifying circuits having impedance, and a tremendous amount of time is consumed.